The present invention relates to call connections in a telecommunications network, and in particular to handling dropped calls in the mobile telecommunications environment.
Cellular telecommunications systems rely on a physical radio link for communications between a fixed base station and a mobile user. A weak signal accompanied by noise and/or distortion, e.g. low signal to noise ratio, in the radio link between the base transceiver station (BTS) and the mobile station frequently results in dropped calls. The communication is eventually terminated because of an inability of the base transceiver station (BTS) and mobile station to communicate with one another. Such radio link failures can be due to, for example, a mobile station entering a region with poor radio coverage, e.g. tunnel, unsuccessful handoff of the mobile communication between different base stations, radio interference from other mobile stations, multipath interference due to multiple radio reflections, unreliable battery connections, and other failures related to software or hardware in the base station.
One of the primary problems with dropped calls is that dropped calls inconvenience mobile telephone users by requiring them to call again, which can result in user dissatisfaction. Furthermore, if dropped calls occur frequently, users may be more reluctant to use their mobile telephones, effectively reducing the amount of revenue that the mobile telecommunication service provider generates.
In most cases, when a call is dropped, no effort is made to recover from the lost connection. Instead, the user of the mobile station must reinitiate the call.
Some solutions for reconnecting involuntarily disconnected calls have been proposed. Industry standard TIA/J-STD-034 describes a proposed solution for connecting dropped emergency calls. The proposed solution, however, is network initiated and involves the network establishing a new connection with the mobile station by calling the mobile station if the call is dropped. One of the main drawbacks of this proposed solution is that, after the network detects that the connection to the mobile station has been lost, the network waits until the mobile station becomes idle and returns to the control channel (i.e., when the user pushes the “on-hook” button on the mobile station) before it can initiate the call back procedure. Then, the mobile station can be paged as a normal call, and the user will receive a ring tone and will have to manually answer the new call. An additional drawback of this proposed solution is that, if the mobile station is no longer within the same coverage area, the network probably will not be able to locate the mobile station to place the new call.
Hellander, U.S. Pat. No. 6,445,918 proposes detecting at the mobile station a radio path loss of a call involving the mobile station; selecting a target cell based on signal quality measurement; transmitting a call reconnect request from the mobile station to the target cell; requesting an identification of a serving switching node involved in the call from a remote database in response to the call reconnect request; and reconnecting the mobile station to the call in response to the call reconnect request. The call reconnect request is sent via a control channel of a target communication station. The control channel and/or its associated target communication station are selected from a neighboring cell list received by the mobile station. In response to the call reconnect request, the network reconnects the mobile station to the call using a radio channel of the target communication station. Hellendar, however, does not disclose a method for handled disconnected call when all base transceiver stations neighboring a mobile station of the disconnected communication have significant path loss to the mobile station, e.g. if the mobile station enters an area of poor coverage.
There is a thus a need and it would be highly advantageous to have, a method and system for handling dropped connections with a mobile telephone within a mobile telecommunications network when the mobile telephone enters an area of poor coverage.